Unitary dual function heat exchanger for gaseous heat carriers



H. A. SAUE'R May 13, 1969 UNITARY DUAL FUNCTION HEAT EXCHANGER FOR GASEOUS HEAT CARRIERS Filed April 14, 1967 /NI/E/V'OP BVCA. SAUEP ff LOM lnlllnlIllllllllnllllllllllll Illlill.

ATTORNEY United States Patent O ice 3,443,632 UNITARY DUAL FUNCTION HEAT EXCHANGER FOR GASEOUS HEAT CARRIERS Harold A. Sauer, Hatboro, Pa., assignor to Bell Telephone Laboratories, Incorporated, Berkeley Heights, NJ., a corporation of New York Filed Apr. 14, 1967, Ser. No. 630,990 Int. Cl. F25d 29/00 U.S. Cl. 165-58 10 Claims ABSTRACT OF THE DISCLOSURE A unitary dual function heat exchanger for a gaseous medium utilizes a mantle with inner and outer evacuated chambers for insulating a heat exchanger cavity. A spiral electrically conductive tube passes through the cavity. In the heating mode, the temperature of the gaseous medium passing through the tube is raised by applying an electric heating current to the tube. In the cooling mode the temperature of the gaseous medium is lowered by a liquid coolant passed through the cavity surrounding the tube.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to heat exchangers and, more particularly, to compound or dual function heat exchangers for gaseous heat carriers.

Description of the prior art The increasingly widespread utilization of heating and cooling sources in modern industrial plants and laboratories has created a growing demand for more eicient heat exchangers and for heat exchangers that are subject to precise control over extremely wide ranges of temperature. Temperature control systems and heat exchangers of the type indicated nd use in particular in the heating and cooling of specimens associated with instrumentation work employing, for example, spectral photometers, microscopes, high frequency dielectric measurement apparatus, thermal diiusivity, specific heating facilities and X-ray equipment. Additionally, convenient and closely controllable sources are required for laboratory work with cryogenic apparatus, including, for example, cryochemical processes and lyophilization procedures such as those encountered in medical and biological laboratories, and in the pharmaceutical and food industries.

Heat exchangers known heretofore are typically designed specically for either heating or cooling. The two functions are generally considered completely separate and distinct, particularly at extreme temperature levels, and, accordingly, it is common practice to employ one type of heat exchanger for heating and a substantially different heat exchanger for cooling. One form of exception to this general practice lies in an arrangement that utilizes a single insulated container for housing essentially separate heating and cooling units. Such a system is shown, for example, by R. Sardeson in U.S. Patent 2,690,327, issued Sept. 28, 1954. In some types of limitedfunction installations such an arrangement may indeed have certain advantages; in general, however, heat exchanger efciency, simplicity and portability are all sacriiiced. Consequently, as an approach to the goal of providing highly convenient dual function heat exchanger equipment, such arrangements fall far short of ideal, especially in view of the lack of portability and general inconvenience necessarily associated with undue size and weight.

Another prior art attempt to solve the problems indicated is shown by H, A. Sauer in U.S. patent application Ser. No. 569,506, tiled Aug. 1, 1966, now Patent No.

3,443,632 Patented May 13, 1969 3,393,729. Sauer teaches a heat exchanger arrangement for a gaseous medium that employs a single mantle or container with a pair of heat exchanger cartridges, one designed for cooling and one designed for heating, either of which may be inserted into the mantle, depending upon the desired mode of operation. Although the twin cartridge concept provides some clear advantages over other prior art arrangements, there is still an inherent, convenience-limiting disadvantage in employing an essentially three-piece unit.

Accordingly, one object of the invention is to simplify heat exchanger equipment that may be utilized for both high level heating and low level cooling.

Another object is to enhance the portability aspects of heat exchanger equipment.

A further object is to enhance the versatility of heat exchangers with respect to the range of temperatures that may be encompassed.

Summary of the invention The foregoing objects and others are achieved in accordance with the principles of the invention by a unitary heat exchanger structure that selectively provides for either the heating or the cooling of a gaseous medium. A key aspect of the invention involves the use of a single electrically conductive tube, which may advantageously be of a coiled configuration, which passes through the central cavity of the heat exchanger. The gaseous medium for which a temperature change is desired is circulated through the tube. In the heating mode, an electrical current is passed through the tube, heating the tube and the gas flowing therein. In the cooling mode of operation a coolant such as liquid nitrogen, for example, is circulated through the heat exchanger cavity, cooling the tube and thus cooling the gas in the tube. Alternatively the cavity may be simply filled 4with a coolant that is maintained at a fixed level. It is evident, therefore, that a heat exchanger in accordance with the invention is indeed a unitary structure in that it employs precisely the same structural elements whether operated in the heating mode or in the cooling mode.

Brief description of the drawing The single figure of the drawing is a sketch, partially in cross section, of a heat exchanger in accordance with the principles of the invention.

Detailed description The heat exchanger assembly 101 shown in the drawing has an outer container or mantle 102 sealed ofi at its input end with a flange 104 and at its output end, by a flange 103. An evacuated outer jacket 105 provides insulation against external ambient temperatures. Additional insulation is provided by a Similar evacuated jacket 106 which is positioned inside the mantle 102. Each of these basic structural members 102 through 106 may advantageously be formed from stainless steel. The end portions of the cavity 128 are partially sealed off by inner flange rings 107 and 108 and lby the substantially toroidal ducts 112 and 113 which function as ange insulating cooling cells. Each of the toroidal ducts 112 and 113 is posititoned around and in intimate Contact with a respective portion of the tube 114 at each end of the cavity 128.

Between the toroidal duct 113 and the inner ange ring 108 is a ilange insulating ring 111 which is preferably formed from an alumina ceramic material. A similar ring 109 surrounds the toroidal duct 112. A commercially available alloy, Kovar, may advantageously be employed inthe fabrication of the ducts 112 and 113. The sealing of the joints between the toroidal duct 113 and the ring 111 and between the toroidal duct 112 and the ring 109 is completed by brazing. Brazed joints of this type typically have an upper temperature limit on the order of 800 C. In accordance with the invention, the temperature of the `brazed joints described is kept below the limit indicated by circulating a suitable coolant, such as liquid nitrogen for example, through the ducts 112 and 113 by means of the tubes 121, 122, 123 and 124.

The central tube member 114 which includes a coiled portion within the cavity 128, has an inlet port 11S and an outlet port 116 extending outside of the heat exchanger proper. An alloy such as Nichrome is a suitable material for the tube 114. For extremely high temperature use platinum or platinum alloys are preferred. The gaseous medium to be heated or cooled is circulated through the tube 114 from the inlet port 115 to the outlet port 116. In the cooling mode of operation a coolant such as liquid nitrogen, for example, is introduced into the cavity 128 by means of an input tube 125, which may also serve as a drain. The coolant circulates through the cavity 128, around the coils of the tube 114 and the exhaust tube 126. Alternatively, the cavity may simply be lled with a coolant that is maintained at some xed level. For the heating mode of operation electrodes 117 and 118 in cornbination with electrical supply leads 119 and 120 provide a means for applying heating current from a suitable source (not shown) to the tube 114. Insulators 127-127 ensure that the end portions of the tubes 121, 122, 123, 124 and 114 are insulated electrically from the center portion of the tube 114 and from the toroidal ducts 112 and 113.

The embodiment described herein employs the single tube 114 as a dual function heating and cooling member. It is evident that this aspect of the invention has a broad potential and may for example be employed to modify a conventional straight multi-tube drum-type heat exchanger so that each of the tubes may serve as a conduit for a uid medium that may be cooled by passing a coolant through the drum and around the tubes or that may be heated by passing an electrical current through the tubes.

It is to be understood that the embodiment described herein is merely illustrative of the principles of the invention. Various other modifications thereto may be made by persons skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A dual function unitary heat exchanger for heating or cooling a gaseous medium comprising, in combination, a central heat exchanger cavity enclosed by a heat insulating mantle, an electrically conductive tube passing through said cavity, means for circulating a gaseous medium through said tube, means for passing an electric current through said tube for operation in the heating mode, and means for filling said cavity with a coolant for operatiton in the cooling mode.

2. Apparatus in accordance with claim 1 wherein a portion of said tube within said mantle is of a coiled configuration.

3. Apparatus in accordance with claim 1 including an evacuated insulating jacket outside of said mantle and an evacuated insulating jacket inside of said mantle surrounding said cavity.

4. Apparatus in accordance with claim 1 wherein said tube is formed from nichrome.

5. A dual function heat exchanger for heating or cooling a gaseous medium comprising, in combination, a central heat exchanger cavity partially enclosed by a heat insulating mantle, an electrically conductive tube, including a coiled portion, passing through said cavity, means for circulating a gaseous medium through said tube, means for passing an electric current through said tube for operation in the heating mode, means for filling said cavity with a coolant for operation in the cooling mode, and partition means within said mantle defining the end boundaries of said cavity.

6. Apparatus in accordance with claim 5 wherein said partition means include a pair of wall members, each of said wall members including a respective substantially toroidal duct member surrounding and in intimate contact with a respective portion of said tube, a respective insulating ring surrounding each of said duct members, a respective sealing joint between each of said duct members and its associated insulating ring, and respective means sealing the gap between each of said insulating rings and said mantle.

7. Apparatus in accordance with claim 6 wherein said sealing joint is brazed.

8. Apparatus in accordance with claim 7 including means for circulating a coolant through each of said duct members thereby to maintain the temperature of said brazed joint below a preselected level.

9. Apparatus in accordance with claim 8 including means for electrically insulating input and output p0rtions of said tube from the portion of said tube within said cavity.

10. Apparatus in accordance with claim 8 wherein said duct members are formed from Kovar.

References Cited UNITED STATES PATENTS 2,723,108 11/1955 Butler et al. 16s- 61 2,979,311 4/1961 Bungas 165-64 3,001,766 9/1961 Laist 16S- 5s XR 3,114,415 12/1963 Wintzer 165-134 XR 3,195,620 7/1965 Steinhardt 165-135 XR 3,306,347 2/1967 Farre 165-58 XR FRED C. MATTERN, JR., Primary Examiner.

MANUEL ANTONAKAS, Assistant Examiner. 

